The world is now facing a climate-driven shrinkage of river-based irrigation water supplies. Mountain glaciers in the Himalayas and on the Tibet-Qinghai Plateau are melting and could soon deprive the major rivers of India and China of the ice melt needed to sustain them during the dry season. In the Ganges, the Yellow, and the Yangtze river basins, where irrigated agriculture depends heavily on rivers, this loss of dry-season flow will shrink harvests. (Read the full report.)

The world has never faced such a predictably massive threat to food production as that posed by the melting mountain glaciers of Asia. China and India are the world's leading producers of both wheat and rice -- humanity's food staples. China's wheat harvest is nearly double that of the United States, which ranks third after India. With rice, these two countries are far and away the leading producers, together accounting for over half of the world harvest.Photo credit: krayker

The Intergovernmental Panel on Climate Change reports that Himalayan glaciers are receding rapidly and that many could melt entirely by 2035. If the giant Gangotri Glacier that supplies 70 percent of the Ganges flow during the dry season disappears, the Ganges could become a seasonal river, flowing during the rainy season but not during the summer dry season when irrigation water needs are greatest.

Yao Tandong, a leading Chinese glaciologist, reports that the glaciers on the Tibet-Qinghai Plateau in western China are now melting at an accelerating rate. He believes that two thirds of these glaciers could be gone by 2060, greatly reducing the dry-season flow of the Yellow and Yangtze rivers. Like the Ganges, the Yellow River, which flows through the arid northern part of China, could become seasonal. If this melting of glaciers continues, Yao says, "[it] will eventually lead to an ecological catastrophe."

Even as India and China face these future disruptions in river flows, overpumping is depleting the underground water resources that both countries also use for irrigation. For example, water tables are falling everywhere under the North China Plain, the country's principal grain-producing region. When an aquifer is depleted, the rate of pumping is necessarily reduced to the rate of recharge. In India, water tables are falling and wells are going dry in almost every state.

On top of this already grim shrinkage of underground water resources, losing the river water used for irrigation could lead to politically unmanageable food shortages. The Ganges River, for example, which is the largest source of surface water irrigation in India, is a leading source of water for the 407 million people living in the Gangetic Basin.

In China, both the Yellow and Yangtze rivers depend heavily on ice melt for their dry-season flow. The Yellow River basin is home to 147 million people whose fate is closely tied to the river because of low rainfall in the basin. The Yangtze is China's leading source of surface irrigation water, helping to produce half or more of China's 130-million-ton rice harvest. It also meets many of the other water needs of the watershed's 368 million people. (See data .)

The population in either the Yangtze or Gangetic river basin is larger than that of any country other than China or India. And the ongoing shrinkage of underground water supplies and the prospective shrinkage of river water supplies are occurring against a startling demographic backdrop: by 2050 India is projected to add 490 million people and China 80 million.

In a world where grain prices have recently climbed to record highs, with no relief in sight, any disruption of the wheat or rice harvests due to water shortages in these two leading grain producers will greatly affect not only people living there but consumers everywhere. In both of these countries, food prices will likely rise and grain consumption per person can be expected to fall. In India, where just over 40 percent of all children under five years of age are underweight and undernourished, hunger will intensify and child mortality will likely climb.

The glaciologists have given us a clear sense of how fast glaciers are shrinking. The challenge now is to translate their findings into national energy policies designed to save the glaciers. At issue is not just the future of mountain glaciers, but the future of world grain harvests.

The alternative to this civilization-threatening scenario is to abandon business-as-usual energy policies and move to cut carbon emissions 80 percent -- not by 2050 as many political leaders suggest, because that will be too late, but by 2020, as outlined in Plan B 3.0: Mobilizing to Save Civilization. The first step is to ban new coal-fired power plants, a move that is fast gaining momentum in the United States (see report).

At issue is whether we can mobilize to lower atmospheric CO2 concentrations before higher temperatures melt the mountain glaciers that feed the major rivers of Asia and elsewhere, and before shrinking harvests lead to an unraveling of our civilization. The good news is that we have the energy efficiency and renewable energy technologies to dramatically reduce CO2 concentrations if we choose to do so.